Indicator tape



United States Patent 3,360,339 INDICATOR TAPE Martin I. Edenbaum, Somerset, N.J., assignor to Johnson & Johnson, a corporation of New Jersey N0 Drawing. Filed Dec. 28, 1964, Ser. No. 421,605 6 Claims. (Cl. 23-253) ABSTRACT OF THE DISCLOSURE An ink is disclosed which consists of a solution of copper sulfite and a film forming carrier, preferably vinyl chloride, in an organic solvent, suitably methyl isobutyl ketone. The ink is ultized to form orange-red markings on various substrates by evaporating the organic solvent, markings which become green in color when exposed to a moist atmosphere and a temperature of 250 for 30 minutes. The ink is therefore particularly adapted for use as, or on devices to be attached to articles which are to be steam sterilized, the device indicating whether or not steam sterilization has in fact occurred.

The present invention relates to color change indicators and more particularly to color change indicators which eifect a color change under sterilization conditions of high temperature and humidity effected during steam sterilization.

In hospitals, clinics and the like, it is standard practice to sterilize various products such as gowns, drapes, sheets, dressings, and other articles, prior to use by placing them in an autoclave where they are subjected to steam sterilization. This practice is necessary to avoid infection and prevent contamination from the use of such articles where the same are not in a sterile condition and is particularly important where the articles have previously been used in the care of other patients. As there is no visual way of determining whether a particular article is sterile or not, it has been the practice to use, with the article, when placed in the steam sterilization chamber, a color change indicator which changes color under the sterilizing conditions of the autoclave, thus indicating that the particular article or package has been passed through the sterilizing cycle. The indicator may be in the form of a ribbon or card to which a color change ink has been applied.

It is generally the practice in sterilizing such articles to gather several articles together, bundling the same in a porous wrap, and then the package, held together by tying with string or by pressure-sensitive adhesive tape, is placed in an autoclave together with a sterilizing indicator, the sterilization indicator may be either inserted in or applied to the package. Where pressure-sensitive adhesive tapes are used for this purpose, it is convenient to have the color change indicator on the tape backing. By observation of the visible back of the tape which holds the package together, one can readily determine by its color change whether or not the same has been passed through the sterilization cycle. Pressure-sensitive adhesive tapes of this type are, for example, described in U.S. Patent No. 2,889,799.

One of the most commonly used color change markings for this purpose are markings containing sulphur and lead oxide. The sulphur in the presence of the lead oxide, under the conditions of the steam sterilization, changes from a yellow to a black color as it is converted to lead sulfide. It has been the practice to mix the sulphur and the lead oxide together in equivalent molar proportions in an ink base which is then applied to an indicator card or to the back of a pressure-sensitive adhesive tape, which, in turn, is then associated with the articles to be sterilized. If the autoclave or other steam sterilizing equipmeat used is not functioning, or if the package to be sterilized inadvertently gets omitted from being placed in the autoclave, this can readily be determined by the fact that no reaction has occurred between the sulphur and the lead oxide as shown by the lack of color change in the indicator.

Although giving a good color change from a light yellow to a deep black with fresh inks, the color change indicator markings made from the active ingredients, lead oxide and sulphur, tend to lose much of their sensitivity over extended periods of storage. This is particularly true under relatively hot or humid conditions. As a result, the ink markings tend to darken appreciably in storage. Also, markings do not turn to the same deep black on being subjected to sterilizing conditions but tend to assume a dark gray appearance, with the result that the color change is not nearly as marked as with fresh inks. Another difiiculty with inks made using sulphur as one of the active ingredients is that the sulphur tends to stain when it comes in contact with many of the new mercurial rinses, such, for example, as phenylmercuric propionate, a material sold under the trade name Velva Soft-G, and presently used in many hospitals as a bactericide. This results in the staining of sheets and other articles making the same somewhat unsightly. The sulphur in the ink also tends to sublime during storage, thus removing part of the sulphur content, and further reducing the eifectiveness of the ink as a color change indicator. Another diificulty with the conventional sulphur lead oxide color change inks is that they are relatively unstable, necessitating the practice of forming separate solutions of the sulphur and the lead oxide and then combining the two together just prior to using the ink for marking. This is apparently due to the fact that the sulphur and lead oxide tend to react while in the solvent medium used in forming the ink. If the ink solution is prepared several days prior to its use, a substantial re duction in color change sensitivity results.

Where the color change indicator is to be used in combination with a pressure-sensitive adhesive tape, as by printing the ink on the back of the tape, the inks containiig the sulphur have the further disadvantage that the sulphur in the marking tends to migrate into the pressuresensitive adhesive where the tape is wound on itself in roll form, thus further reducing the sensitivity of the marking to color change, when the tape, with the ink marking thereon, is later exposed to steam sterilization conditions.

Despite these inherent disadvantages in color change markings using sulphur and lead oxide, such markings have continued to be used as steam sterilization indicators, as they were still superior to other known color change indicators for indicating steam sterilization.

It is an object of the present invention to make color change indicators which will give a marked color change under steam sterilizing conditions and which are stable over extended periods of storage under normal atmospheric conditions. It is a further object of the present invention to prepare inks in which the color change pigments are stable for extended periods of time while still in the liquid ink medium, and from which markings can be made which are stable to color change under normal atmospheric conditions. It is a still further object of the present invention to prepare color change markings free from the deficiencies previously mentioned which are present in color change markings in which free sulphur and litharge are the primary active ingredients. Other objects and advantages of this invention will become apparent from the following description wherein are set forth by way of illustration and example certain embodiments thereof.

3 3 It has now been discovered that excellent color change markings can be made by using copper sulfite as the primary color change ingredient in a moisture pervious film-forming carrier.

It has been found that, when a marking is made from a dispersion of finely divided copper sulfite in a steam permeable colorless carrier, a very interesting and marked color change occurs when the marking is subjected to steam sterilizing conditions. The color of the marking is initially orange-red prior to steam sterilization. Red is a color that has been used for many years as a signal of danger and, aptly in the present instance, gives the danger warning that the article to which the marking is applied has not been subjected to steam sterilization. However, when heated in the presence of steam to a temperature of about 250 F. for a period of about 30 minutes, which are excellent steam sterilizing conditions, the color changes to a pastel green. This color change to green is a very appropriate color change, as green is a color long used in opposition to red to indicate clearance, that the situation is now cleared of danger. Thus the color change obtained clearly indicates safety, that the article containing the marking has been subjected to steam sterilization.

Although showing excellent stability under normal atmospheric conditions and under dry heat conditions, even at temperatures as high as 300 F., when heated for half an hour in a steam atmosphere of 250 F., a sharp color change occurs from the basic red of the marking to a pastel green color.

The copper sulfite is applied in an ink base containing a film-forming carrier for anchoring the pigment to a substrate, after the solvent medium used in the ink has evaporated. Although various film-forming resins may be used for this purpose, vinyl resin carriers, such for example as Bakelite Resin VYHH, a copolymer of polyvinyl chloride and polyvinyl acetate, have been found to be particularly suitable. The concentration in the ink of the copper sulfite is not particularly critical, although there should be sufiicient copper sulfite to give a clearly visible marking. In the preferred practice, the color change pigment is present in amounts of about 0.5 to 3 parts by weight per part by weight of the resin carrier.

Any solvent may be used for the resin film-forming carrier in making up the ink solution. Methyl isobutyl ketone, hereinafter referred to as MIBK, is an excellent solvent for this purpose, particularly where the filmforming resin carrier is a vinyl resin such as Bakelite Resin VYHI-I.

The film-forming resin carrier used must be one which is permeable to steam, in order to obtain a satisfactory color change under steam sterilizing conditions. Where the resin film-forming carrier does not of itself have sufficient permeability to steam, it can be made satisfactorily permeable by adding to the ink a small amount of Wetting agent of either the anionic or cationic type. Non-ionic wetting agents do not appear to be satisfactory for this purpose.

As the color change indicator of the present invention is quite stable to dry heat, even at temperatures as high as 375 F., the color change inks are well suited for the preparation of temperature indicator tapes of the type described in Patent No. 2,889,799, where the pressure-sensitive adhesive of the tape is a heat cured pressure-sensitive adhesive where curing is to be done prior to use of the tape. As curing temperatures for such pressure-sensitive adhesives is frequently as high as 300 F., any color change indicator not showing substantial stability under dry heat conditions at such temperature is not fully satisfactory, as a substantial amount of the sensitivity to color change of the ink is lost during the curing of the pressure-sensitive adhesives. The color change indicator inks of the present invention are thus particularly well suited for the preparation of temperature indicator pressure-sensitive adhesive tapes, wherein the color change indicator is carried by the tape.

As the color change is from orange-red to a pastel green, the change in color is readily identified. Also, the initial red and the later green color clearly point out to the user whether or not the sterilizing conditions have been met.

The invention is further illustrated by the following example which is given for the purposes of illustration only, the invention not being limited thereto.

Example I A vehicle of the following formulation is prepared:

Parts Bakelite resin VYHH 1.0 MIBK (methyl isobutyl ketone solvent) 2.75

parts where used refers to parts by Weight.

Into parts of this vehicle are ground on a three roll ink mill: Copper sulfitc-35 parts.

This paste is diluted with an equal weight of MIBK to give a thin, orange-red liquid of the proper viscosity for intaglio printing.

The ink so prepared is gravure printed on a 30# stock paper which has been surface coated with a white pigmented nitrocellulose lacquer. The print roll used is engraved with a pattern of small diamonds arranged in straight rows running at an angle of 60 to the direction of travel of the paper. The printed sheet is passed through a drying oven set at 150 F. to fiash oil the solvent.

In subsequent steps, the printed paper is top coated with a release coating of Quilon, a water soluble Wernertype chrome complex dissolved in isopropanol and described in Dupont Bulletin Quilon Chrome Complex, Bulletin #A18204. The sheet is then mass coated on the opposite side with a pressure-sensitive adhesive of the conventional rubber base type. In both steps, drying temperatures of 200250 F. for one minute are used.

Rolls of tape prepared in the manner described are placed in storage at normal atmospheric conditions (RT Storage) and in a room kept at F. The tape samples are tested regularly for eight months, with the following results:

RT Storage Ink Color Ink Color Months in Before Auto- Alter Auto- Storage claving claving 250 F., 30 min.

0 0rangc-red. Pastel green.

Do. Do. Do. Do.

120F. Storage Orange-red Pastel green.

- Do. D0. Do. Do.

Particular embodiments of the invention have been used to illustrate the same. The invention, however, is not limited to these specific embodiments. In view of the foregoing disclosure, variations or modifications thereof will be apparent, and it is intended to include Within the invention all such variations and modifications except as do not come within the scope of the appended claims.

Having thus described my invention, I claim:

1. In a steam sterilization indicating device of the type comprising a base and containing a marking thereon which changes color when exposed to the conditions of steam sterilization the improvement comprising: said 6. An ink of claim 5 in which said film-forming resin is a copolymer of polyvinyl chloride and polyvinyl acetate.

References Cited UNITED STATES PATENTS 1/1959 Korpman 116114 OTHER REFERENCES Sneed et al.: Comprehensive Inorganic Chemistry,

10 pp. 104-105, Van Nostrand, N.Y., 1954.

MORRIS O. WOLK, Primary Examiner. L. MEI, Assistant Examiner. 

1. IN A STEAM STERILIZATION INDICATING DEVICE OF THE TYPE COMPRISING A BASE AND CONTAINING A MARKING THEREON WHICH CHANGES COLOR WHEN EXPOSED TO THE CONDITIONS OF STEAM STERILIZATION THE IMPROVEMENT COMPRISING: SAID MARKING COMPRISING A STEAM PERMEABLE CARRIER FILM CONTAINING COPPER SULFITE MONOHYDRATE. 